Bernie Sanders’ revolution may be growing directly from the grass roots, but he’s paying top dollar for the places where it’s coming together.

In February, the Sanders campaign, flush with cash from its small-donor network, spent $1.6 million on site rentals, ticketing and “sound/stage/lighting,” pursuing ever-larger venues for his followers to gather in, according to Federal Election Commission filings.

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And the spending this month may well exceed February. On Friday, for instance, the Sanders campaign is staging a pep rally for the Washington state caucuses at Safeco Field in Seattle, the Mariners’ baseball stadium that holds up to 54,000 people.

It's a sign that the Sanders campaign plans to keep spending big as it works to compete with former Secretary of State Hillary Clinton across the board.

Last month, Sanders paid to staged campaign events in such large venues as the Colorado Convention Center ($23,000 total) and Eastern Michigan University Convocation Center (about $18,150). The end result was, according to the Sanders campaign, 18,000 people in attendance in Denver and 9,400 people coming to see the senator at EMU. He won both states' Democratic contests in February.

"I would say it's more like what you would be spending in a general election because of the size of your crowds," Bob Shrum, a former senior adviser to John Kerry's presidential campaign, said of Sanders' event spending. "But he's getting crowds of that size in the primary. So you've gotta have those venues, and you gotta do the lighting and the stagecraft so that people in a place where there are eight or 10 or 12,000 people can actually see the stage and the candidate."

Sanders appears to be spending more than Clinton and the remaining GOP candidates mainly because he can. Fueled by small donations, he raised $43.5 million in February and ended up with $17.2 million cash on hand, according to his FEC report. By contrast, Clinton raised $30 million and ended the month with $31 million cash on hand. All the GOP contenders raised less.

Some of Sanders’ haul has gone to payroll, lodging and consulting, but large chunks have also gone to travel and Bernie swag.

Sanders spent $1,659,181 on charter flights in February, according to the most recent report, a month when the candidate had to jet among the Super Tuesday states. By comparison, in the third quarter of 2015 former Florida Gov. Jeb Bush spent about $920,000 on private jets, and total spending on air charters in that period for all the candidates was $2.5 million.

Sanders also spent about $625,000 on campaign paraphernalia, most of which was produced by Western-Ohio based Tigereye Promotions LLC, which has been the primary producer for Sanders' online store on his campaign's website. About $622,000 went to Tigereye, which produces T-shirts, buttons and Sanders signs. "Sanders for President" T-shirts, especially one designed by artist Shepard Fairey — creator of the iconic Obama image — have been the the most popular items, Tigereye President Monica Baltes said.

"We also take care of another segment of items for them to go out to the field offices. So if they're having a campaign rally in Arizona and we have rally signs and stickers here, we will ship those things to those places as well," Baltes said.

One area in which Sanders wasn't very spendthrift was catering. His February campaign bill was only about $49,000 on catering, including about $620 on Chick-fil-A, $1,140 on Subway and $1,088 on Panera Bread.

As the Sanders campaign has grown, so too has its budget for direct mail and media buying — $19.9 million of the campaign's spending in February went to buying ad slots, with another $838,000 devoted to direct mail. The campaign pays a trio of liberal consulting firms as well: Revolution LLC, a digital messaging firm that reaped $3,363,000 in February; Solidarity Strategies, a direct mail firm that received $958,000; and Devine Mulvey Longabaugh, the consulting shop for Tad Devine, Sanders' chief strategist, which received $810,000.

Bernie Sanders boards his campaign plane on Feb. 12. | AP Photo

Sanders also spent $767,000 on Tulchin Research, the consulting firm of Sanders pollster Ben Tulchin. That's an increase from January, when Tulchin's firm received about $542,000. Through most of 2015, Sanders had resisted bringing a pollster on full time, saying he wasn't going to tailor his message to what day-to-day polls said was popular. But Devine persuaded Sanders to sit down with Tulchin in the fall of 2015. Tulchin formally announced joining the Sanders campaign in January.

"I suspect a lot of that was to try to figure out" which states to target, Shrum said of the campaign's polling budget. "Because if you target the wrong state you're wasting a lot more money than the pollster cost."

Both Sanders' fundraising and spending were up significantly from January, when his campaign raised $20 million while spending $32.4 million. Sanders ended that month with $28.3 million cash on hand.

By the end of February, Shrum noted, it was no surprise that Sanders finished the month with less cash on hand than Clinton despite having raised more: He's using his bank account to try to catch up.

"He's clearly the underdog," Shrum said. "He has a mission and a cause that I think can sustain him not only through California but through the convention. And he has the resources, but to make that enterprise work you got to keep holding these big rallies, you've got to advertise in these states, you've got to win delegates."

Sanders, he added, is trying to "run a campaign that does not look like it's running out of energy, doesn't look like it's scaling back in terms of its reach toward folks, that's not shedding organizational assets. And it seems to me that he can do this because they just seem to be able to raise money."